the present invention relates to a recording apparatus for forming a visible image on a photoconductive drum, paper or like recording medium by using a liquid developer of black or like single color or liquid developers of a plurlity of chromatic colors such as red, green and blue. More paticularly, the present invention is concerned with an arrangement for preventing the mono-color developer or the multi-color developers from overflowing containers in which they are accommodated.
Typical recording apparatuses of the kind described includes an electrophotographic color copier and a color ink jet printer. Considering an electrophotgraphic color copier, for example, one type of conventional ones is constructed and arranged to selectively supply liquid developers of different colors, e.g., black, red, green and blue to a single developing unit, as disclosed in Japanese Patent Publication No. 54-43898. In this type of semi-moist process color copier, as in a monochromatic semi-moist process copier, there are installed a diluent vessel for causing a diluent to automatically flow down into each developer vessel when a liquid level in the vessel is lowered, and a developer container for supplying the developer vessel with a high-concentration liquid developer by opening an electomagnetic valve when he concentration oft he liquid in the vessel is reduced.
Usually, the proportion of an image area to a non-image area on a document surface is very small. If follows that the developer (e.g. toner) is supplied to and consumed by a paper or a drum at a rate which is substantially equal to or lower than a rate at which the diluent is supplied to and consumed by a paper or a drum. In this condition, the developer vessel is prevented from overflowing even if supplied with the high concentration developer. Meanwhile, where an original document with solid content or a one with a high image rate is copied continuously, the toner consumption rate int he liquid developer is increased and, therefore, the concentration of the developer is sharply lowered. Such a decrease in the developer concentration needs be coped with by frequent supply of the developer which would increase the amount of developer in the vessel and, thereby, cause the developer to overflow the vessel. Once possible approach to prevent an overflow is using a sensing device sensitive to an upper limit of the liquid level and interrupting the operation of the copier as soon as the device senses the upper limit level. Such a sensor scheme, however, cannot be implemented without degrading the performance of the copier.
An electrophotographic color copier usually has a capability of producing a copy selectively in any of four different colors in total, e.g. black, red, green and blue and in a mixture of such colors. In this case, a black liquid developer is circulated from its associated vessel through a cleaning unit so as to clear the surface of a photoconductive drum of residual toners of the respective colors, the residual toners and black developer being collected and returned to the black developer vessel. In the event of changing the recording color, a cleaning liquid is fed to a developing unit to clean it and, then, a liquid developer of a specified color is supplied to the unit.
In the above-described construction wherein residual toners are collected by the cleaning unit to be returned to the black developer vessel with no regard to the recording colors, a grater amount of developers than a one which is consumed by development in black is returned to the black developer reservoir due to repetition of recordings in colors other than black. The resultant increase in the amount of developer in the vessel would cause the vessel to overflow. Needless to mention, where the frequency of producing a copy in black with a high image rate is relatively low while the frequency of producing copies in other colors each with a high image rate, it might occur that liquids of those other colors overflow their associated vessels.
Apparently, increasing the size of the various developer vessels is a possible implementation for settling the problematic situation as discussed above. This, however, would result in an increase in the dimensions of the whole apparatus.